The present invention relates to inorganic matrix compositions, which incorporate a silicate network and which can be processed at conditions comparable to those used for high-performance organic polymer processing, i.e., temperatures of about 15° C. to about 200° C. and pressures of less than about 200 psi, although a wide range of temperatures and pressures can be employed. The physical and thermal properties of the inorganic matrix binder, as well as composites, may be enhanced by elevated processing temperatures (up to 400° C. and greater) and pressures (up to 20,000 psi and greater) to produce exceptional neat resin and composite components. The composite materials formed at the lower processing conditions exhibit excellent thermal, dimensional, physical and flameproof properties.
The basic concept of composite materials has been known for centuries. Composite materials offer a unique blend of value added features, such as weight savings, electrical insulation, thermal insulation, corrosion resistance, and manufacturing cost savings. These features in some instances can overshadow the material cost in specialized applications ranging, for example, from sporting equipment to the F-22 aircraft fuselage. However, current state-of-the-art composite materials can also exhibit properties that present serious barriers to entry in some high-performance markets. These include poor flame, smoke and toxicity (FST) performance, physical degradation at high temperatures as well as higher material and processing costs. When exposed to fire or high temperatures (>500° C.), conventional composite materials can combust and generate toxic smoke and/or gases. The exceptions, such as ceramic matrix composites and metal matrix composites, are too expensive (often more than $500/lb) to gain a significant market presence. Clearly, a market need exists for affordable high temperature-resistant, insulating structures which have potential applications that minimize fire and heat transfer damage to sensitive areas, aircraft carrier blast or heat shields, high-temperature (600° C.) thermal insulation for wiring or other sensitive components susceptible to thermal damage, piston insulators, high temperature insulating structures, and fire barriers.
The most familiar composite systems today are based on organic polymer matrices such as epoxy/glass fiber, epoxy/carbon fiber, polyurethane/glass fiber, PVC/glass fiber, polyimide/quartz fiber, polyester/glass fiber and nylon/glass fiber. The flammability of organic polymer-based composites can be reduced by the addition of inorganic components and/or additives. The substitution of hydrogen atoms with halogen atoms (e.g. chlorine) in hydrocarbons and hydrocarbon polymers can significantly reduce flammability and smoke/gas generation but will degrade at high temperatures (>250° C.) and eventually incinerate at higher temperatures (>450° C.). Organic thermoplastic polymers also deform at relatively low temperatures (about 100° C.-300° C.) and organic polymers designed for higher service temperatures are generally prohibitive in material and processing costs.
Other composite materials include metal matrix composites (MMC), ceramic matrix composites (CMC), carbon-carbon composites as well as other inorganic matrix composites. A composite matrix may be 100% inorganic, or it may contain some organic content. Inorganic matrix networks include ceramics, silicates, glasses, aluminum silicates, alkali aluminum silicates, potassium silicates, sodium silicates, silicon carbides, silicon nitrides, alumina, cementitious materials, metals, metal alloys or other matrix materials known to those knowledgeable in the arts. Other materials that can be considered include inorganic particles encapsulated with inorganic binders, organic resins filled with inorganic fillers, inorganic-organic hybrids such as silicone, and other inorganic matrix materials known to those knowledgeable in the arts.
A disadvantage of organic polymers is their deficiencies at high temperatures. The use of metals and ceramics raises additional questions with regard to thermal and electrical conductivity, weight limitations, toughness, dielectric properties, ductility, and processing options. Further, ceramics do not lend themselves to the low temperature processing procedures as contrasted with organic polymer processing.
Alkali silicates are employed as affordable inorganic matrix binder materials. See for example, U.S. Pat. Nos. 4,472,199; 4,509,985; 4,888,311; 5,288,321; 5,352,427; 5,539,140; or 5,798,307 to Davidovits; U.S. Pat. No. 4,936,939 to Woolum; or U.S. Pat. No. 4,284,664 to Rauch. However, alkali silicates possess a high pH, which can frequently damage glass fibers by both chemical and physical means, severely degrading its strength. Furthermore, the cured composites taught by these patents still exhibit a high pH in a solid form, which continues to promote glass fiber degradation. So, the physical performance of a fiberglass/alkali silicate composite usually is extremely poor. This has been compensated by reinforcing the alkali silicate matrix with carbon fiber reinforcements rather than fiberglass. This replacement suffers in comparison to a composite prepared with fiberglass reinforcement in several respects such as material cost since carbon fibers are several times more expensive than glass fibers. Carbon fibers are also electrically and thermally conductive, which eliminates many important dielectric and thermal insulating applications and carbon fibers severely oxidize at 450° C., which eliminates many important high temperature applications. Also, when carbon fibers are combined with the alkali silicate matrix they have two different thermal expansion coefficients, which can lead to microcracking during thermal cycling.
Furthermore, cured alkali silicates (including alkali aluminum silicates) are also caustic when exposed to moisture, yielding a caustic solution, which is undesirable. Caustic by-products may accelerate corrosion in adjacent materials, in many applications, and the extreme caustic nature of the cured material suggests hydrolytic instability. Improved inorganic matrix materials that are less caustic may enable a much broader range of applications.
Thus, a need exists for noncombustible, temperature-resistant inorganic polymer compounds which process at temperatures and pressures typical for organic composites (<200° C. and <200 psi) in combination with the desirable features of ceramics (non-flammability and resistance to temperatures >450° C.) and complex shapes achievable with organic polymers.